1. Field of the Invention
The present invention relates to conservation of auxiliary battery power in adapters. More particularly, it relates to an apparatus and method for conserving auxiliary battery power in a wireless device that is connected to a host device.
2. Description of the Prior Art
Wireless devices enable computers to communicate with other computer devices without requiring physical access to a land line communication port. One type of wireless device is a wireless modem which is similar to a wired modem in that it permits a computer or other device to send and receive data from external sources. A wireless modem may be installed as an adapter card or in an adapter slot such as a Personal Computer Memory Card International Association PCMCIA slot. A wireless modem typically consists of two major portions: a radio portion and a baseband portion.
The radio portion consists of a transmitter and a receiver. The transmitter and receiver may share a common antenna via a duplexer. The transmitter is responsible for generating RF signals using a baseband signal to modulate a carrier signal. The receiver is responsible for producing a baseband signal from RF signals by demodulating an RF signal received at the antenna to produce a demodulated baseband signal. The radio provides physical access to a network or connection (i.e., the wireless network). An antenna is used for transmitting and receiving the electromagnetic communications signals from the air interface.
The baseband portion provides a baseband signal to the transmitter and accepts baseband signals from the radio receiver. The baseband portion decodes the baseband signals to provide data (i.e., receiving data) and encodes data to provide a baseband signal for transmission by the transmitter (i.e., sending data).
As is typical of wireless modems, a portion of the wireless modem fits into a PCMCIA adapter slot. The adapter may consist of an integrated package or several separate components that can be attached via appropriate cabling. The radio portion of the wireless adapter contains the transmitter, receiver and associated circuitry to provide for RF communications. The ability of the radio to transmit at certain ranges is limited by the transmit power it can radiate via the antenna. The radio transmitter can require substantial amounts of current (as much as 1 amp) to operate. Most wireless systems require that the transmitter radiate power at levels up to 3 watts. The transmitted power levels in some wireless systems are controlled by the base station transmitter. The radiated power level can thus require that approximately 1 amp of current be supplied to the radio transmitter of the wireless modem when the wireless modem is radiating at higher power levels. Typically transmit power levels for Advanced Mobile Phone Service (AMPS) cellular and Cellular Digital Packet Data (CDPD) transmissions are 600 mW. For Advanced Radio Data Information Service (ARDIS), transmission levels of 1 W are typical.
The PCMCIA architecture can typically only supply a PCMCIA slot with a 1/2 amp (500 mA) of current. This limitation is due to the nature of the PCMCIA interface and the PCMCIA standard itself. Therefore, with wireless adapters the PCMCIA bus of the host computer can supply less than half the required current when the radio transmitter is operating at higher power levels. In order to provide the required power, prior art systems have supplemented the power supplied to the radio with an auxiliary battery or batteries. These prior art systems have directly coupled the auxiliary power source to the transmit amplifier.
Use of the auxiliary battery creates several problems, especially for laptops or mobile computing devices. First, the auxiliary battery is inconvenient for mobile computer users to carry (i.e., 4AA NiCAD batteries). This inconvenience is caused by the bulk and weight of the auxiliary battery. The bulk of the auxiliary battery also makes the mobile device unwieldy to place and utilize. Secondly, the auxiliary battery needs to be periodically recharged. Auxiliary battery re-charging, in addition to any host battery recharging, is an inconvenience for user. The wireless adapter's recharging unit may be incompatible with the recharging system for the laptop thus forcing the user to carry two different recharging mechanisms: one for the mobile unit's battery and one for the adapter's auxiliary battery. Thirdly, prior art systems directly coupled the auxiliary battery to the transmitter's power amplifier. This caused the wireless adapter to be inoperable under any operating conditions when the auxiliary battery needed recharging. Thus, there is an unsatisfied need in the prior art to reduce the size of the auxiliary battery and/or increase the time periods between recharging. There is also a need to permit wireless adapters to operate in certain circumstances with a dead or defective auxiliary battery.
These unresolved problems and deficiencies are clearly felt in the art and are solved by the invention in the manner described below.